1. Field of the Invention
This invention relates generally to a commutatorless motor device, and more particularly to a type thereof wherein induced voltages of a synchronous motor are utilized for detecting the rotor position, and the motor is thereby operated at a predetermined margin angle regardless of variation in stator current.
2. Description of the Prior Art
A commutatorless motor device is known wherein the angular position of the rotating magnetic field is detected by a proximity switch or the like, and the commutation of the stator current is controlled by the thus detected position indicative signal. This type of commutatorless motor device, however, cannot compensate for the shifting of the rotating magnetic field due to the armature reaction, and the power factor and operational efficiency of the device are deteriorated during the light-load condition, thereby increasing the torque ripple.
Recently, there has been developed a control system of commutatorless motors, wherein the position of the rotating magnetic field is detected directly from the counter electromotive force of the motor, and the stator current is commutated under the control of the thus detected positional signal so as to compensate for any harmful effect of the armature reaction.
In this case, however, since the amptitude of the counter electromotive force changes according to the magnitude of rotational velocity of the rotor, the induced voltage detected during rotation of the motor at low velocity can be very small and to detect exactly the counter electromotive force is difficult. Accordingly, it has been impossible to sufficiently improve the output characteristic of the motor.
Further the margin angle of commutation for the control system for the commutatorless motor is varied by the load condition of the motor, thus deteriorating the output characteristics of the motor, particularly in its light-load condition.